TORONTO (Reuters) - Shares in Canadian e-commerce company Shopify Inc <SHOP.TO> dropped on Tuesday despite its better-than-expected earnings, with concerns about future growth and lack of fresh disclosures rattling investors after a recent short-seller attack.

Investors and analysts had hoped Shopify would release more details about its operations and customers after Andrew Left of Citron Research released a critical report about the retail software company in early October.

Shopify founder and Chief Executive Tobi Lutke said on a conference call to discuss the results that the company's external legal counsel had dismissed Left's claims as "preposterous" and that it had not been in contact with the U.S. Federal Trade Commission (FTC) following the report.

Fast-growing Shopify's third-quarter revenue jumped 72 percent and it reported adjusted profit for the first time as a public company, a quarter earlier than it had suggested as likely, but forecast slower revenue growth in the fourth quarter.

Shares in Ottawa-based Shopify fell as much as 13.6 percent on Tuesday morning.

Left has complained about payments to bloggers and others who get merchants to sign up to Shopify's commerce platform and suggested the FTC should investigate the company.

Citron said in a statement on Tuesday it was unimpressed by Shopify's response. It added that it has sent some material to U.S. regulator FTC and is certain Shopify will face investigation for selling business opportunities.

FTC did not offer any comment when reached by Reuters.

By midday, the shares were down 10 percent, while the benchmark Toronto exchange was up 0.3 percent.

"The initial reaction from investors seems to suggest that they didn't go far enough in their explanation," Tom Forte, an analyst with D.A Davidson, said.

The company did not provide any additional operational metrics. Left had asked for Shopify to disclose what portion of its merchants drop off the platform each month.

RBC Capital Markets analyst Ross MacMillan said the market had been anticipating more upside, taking the shine off of Shopify's earnings beat.

"In other words, they beat numbers, but beat them by less than they had been beating them," he said.